There are two main types of chemical disinfection systems for contact lenses, multipurpose and hydrogen peroxide-based systems. Hydrogen peroxide-based systems are often preferred, due to its rapid kill of microbial contaminants, preservative-free packaging, low user sensitivity, and neutralization to natural by-products, such as water and oxygen. The disadvantage of the hydrogen peroxide-based systems are that they require memorization of what time the disinfection time was started and figuring out when the neutralization process is complete. Also, if too much time has elapsed since the hydrogen peroxide solution has been neutralized, the sterile solution can eventually become re-infected and foster microbial growth. One of the main reasons why users switch from hydrogen peroxide-based systems to multipurpose is because hydrogen peroxide-based systems require users to calculate when the ideal usage time is for each time that they disinfect their contact lenses, without knowledge of how effective the platinum catalyst is working; that is, enough elapsed time has passed to ensure the peroxide has been fully neutralized, to avoid chemical conjunctivitis and keratitis, and short enough elapsed time to ensure microbes have not re-infected the sterile solution.
An example of a contact lens cleaning and sterilization system is described in U.S. Pat. No. 4,687,997. This cleaning system requires insertion of the lenses into a disinfecting solution for a preset time period followed by insertion into a neutralizing solution for a second preset time period. A first indicator shows a steady light while the disinfectant is in the cleaning case and a second indicator when the neutralizing solution is in the case. The system distinguishes the disinfecting solution from the neutralizing solution by measuring the electrical conductivity of the solution within the cleaning case. After a predetermined amount of time, both lights flash to indicate the item has been disinfected and neutralized, respectively. This system does not monitor the efficacy of cleaning, disinfecting or neutralization of the solutions, however; the indicator lights flash to show completion of the disinfecting and neutralization cycles solely in response to the passage of time.
Another example of a cleaning and sterilization system is described in U.S. Pat. No. 6,183,705. The system uses ultrasonic waves to clean contact lenses, and heat to disinfect contact lens solution medium. The system includes a housing, control circuit assembly, ultrasonic waveguide, a heating rod with two electrodes and a graduated cleaning cup that is operated using the automatic control circuit. The control circuit includes a microprocessor for controlling the heating rod and the ultrasonic waveguide. The microprocessor operates the ultrasound transducer for a preset time, then stops. After a rest time, the microprocessor heats the cleaning solution to a preset temperature of 90° C. as measured by a temperature sensor, then turns off the heating rod, allowing the lenses to soak in the hot solution for another preset time. Once again, this system does not monitor the efficacy of the cleaning solution; the cleaning process always proceeds along the same preset time intervals, and the indicator lights merely show which stage the cleaning process is in.